Fix for ticket #2942: character counter now updates on cut and paste operations made with mouse or menu

This uses the 'copy' and 'paste' DOM events to trigger a counter update. I haven't had a chance to 100% confirm that middle-button click on X11 triggers the event, but it ought to.
Cut and paste events from context menu and main edit menu known good in:
* Firefox 4.08b-pre
* IE 9 preview 7
* IE 8 current
* Chrome 8 beta current
* Safari 5.0.3

Opera is listed as not supporting these events, oh well.

Note that using a *delete* command from a menu doesn't trigger an event. Sigh, you can't win everything.

js/util.js

@@ -85,6 +85,19 @@ var SN = { // StatusNet
                     SN.U.Counter(form);
                 });
 
+                var delayedUpdate= function(e) {
+                    // Cut and paste events fire *before* the operation,
+                    // so we need to trigger an update in a little bit.
+                    // This would be so much easier if the 'change' event
+                    // actually fired every time the value changed. :P
+                    window.setTimeout(function() {
+                        SN.U.Counter(form);
+                    }, 50);
+                };
+                // Note there's still no event for mouse-triggered 'delete'.
+                NDT.bind('cut', delayedUpdate)
+                   .bind('paste', delayedUpdate);
+
                 NDT.bind('keydown', function(e) {
                     SN.U.SubmitOnReturn(e, form);
                 });